Display screen or portion thereof with a graphical user interface of a mobile device



FIG. 1 is a front view of a first embodiment of a display screen with a graphical user interface of a mobile device; and,

FIG. 2 is a front view of a second embodiment of a display screen with a graphical user interface of a mobile device.

The broken lines illustrate the display screen or portion thereof and form no part of the claimed design. The broken lines illustrate portions of the graphical user interface and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface of a mobile device, as shown and described. 